C-scan, which is one of the results based on an ultrasonic testing (UT) technique from among techniques of detecting defects in structures, shows an excellent result in detecting defects in structures, and thus is being used in many industrial fields. However, the conventional ultrasonic testing technique requires much time as it uses couplant and a contact transducer. In addition, in recent years, noncontact ultrasonic testing is conducted through an air-coupled transducer, but an inspection distance is a few centimeters and thus there is a limit to the inspection.
Recently, a method which generates ultrasounds of a wideband on a surface of a structure through a laser ultrasonic generator of a thermoeleastic mechanism, and uses ultrasounds generated in the structure is actively studied and researched.
Since the current researches and techniques use a single point as an ultrasound source and utilize ultrasounds propagated in an in-plane direction, an in-plane damage or defect is not exactly detected, and also, information on through-the-thickness defects is not provided.
Therefore, there is a need for a method for visualizing information of through-the-thickness defects in a full field.